Thymopoietin is a polypeptide hormone of the thymus that induces differentiation of prothymocytes to thymocytes and also has secondary effects on neuromuscular transmission. Two forms of bovine thymopoietin, designated thymopoietin I and II have been isolated and shown to be immunologically cross reactive. (Thymopoietin is now used in preference to the original name Thymin). See G. Goldstein, Nature 247, 11 (1974).
Although thymopoietin can be detected by bioassay using either its effects on T cell differentiation or neuromuscular transmission, these assays are complex, timeconsuming, and difficult to standardize. Moreover, unlike immunoassay, and particularly radioimmunoassay, bioassays are not readily automated and thus could not be routinely employed by clinical laboratories or other diagnostic facilities to screen large numbers of samples in an economic fashion.